Observations

Description

Valves are moderately arched. The dorsal margin has three broadly rounded undulations, with the number of undulations consistent across large to small valves. The ventral margin is concave and follows the same curvature as the dorsal margin. The apices are protracted, broadly rounded and more narrow than the undulations. Distal raphe ends are curved toward the dorsal margin close to the valve ends. Striae are radiate throughout and are of two types: 1) complete striae that extend the width of the valve and 2) short striae that are interspersed between complete striae along the dorsal margin. A fine hyaline line is near and parallel to the ventral margin. Striae on either side of this line may be aligned or displaced. Areolae in the striae number 27-30 in 10 µm.

Eunotia triodon has moderately arched valves with three broadly rounded, rather than deeply rounded, undulations on the dorsal margin. Apices are protracted and broadly rounded, but more narrow than the undulations.

Compare

Eunotia triodon may be distinguished from other large species of Eunotia with dorsal undulations by its moderatly arched valves and a consistent three broadly rounded undulations on the dorsal margin. Eunotia semicircularis may also have three undulations, but they are deeper undulations than E. triodon. Note that the degree of undulation (broad vs. deep) may be more relevant to identification than the number of undulations in distinguishing taxa.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

North American Diatom Ecological Database (NADED)

NADED ID: 33063

Autecology Discussion

Eunotia triodon is uncommon in the Northern Rockies and North Cascades. The specimens shown here are from Blodgett Lake in the Bitterroot Mountains of western Montana and Cutthroat Lake in northern Washington (photos below). Blodgett Lake is at an elevation of 3,000 m. Here pH measured 6.50 and specific conductance was 7 µS/cm.